1. Field of the Invention
The present invention relates generally to the control of an internal combustion engine having an air introduction device in the engine exhaust.
2. Background of the Invention
Vehicle engines have used a secondary air pump in the engine exhaust to introduce air to increase emission control. The pumps are attached, for example, to the exhaust manifold of the engine and pump ambient air into the exhaust. The secondary air can react with rich exhaust gasses to rapidly heat the catalytic converter. Further, schemes have been developed for estimating the airflow introduced via the secondary air pumps. An example of such a system is described in U.S. Pat. No. 6,044,643.
The inventors herein have recognized a disadvantage with the above approach. In particular, as vehicle conditions change and components age, accuracy of open loop estimates can vary. Degradation in the estimate of airflow introduced via a secondary air pump can result in degraded emission control. This is especially true in a system that attempts to exothermically react rich exhaust gasses with secondary air. In other words, if the estimate of airflow is inaccurate, the overall mixture may provide incomplete exothermic reaction, resulting in degraded emissions.
The above disadvantages are overcome by a method for controlling engine operation, the engine having an exhaust system including an air introduction device and an exhaust gas sensor. The method comprises: after an engine cold start, operating the engine with a rich air-fuel ratio and adding air via said air introduction device; and during said operation: estimating an air amount introduced into the exhaust from said air introduction device based at least on an operating condition and an adaptively learned parameter; determining if the sensor is operating; in response to said determination, updating said adaptively learned parameter based on said exhaust gas sensor; and injecting a fuel injection amount into the engine based on said estimated air amount.
By using an adaptive approach, it is possible to correct for variations in pump flow due to pump aging, changing conditions in parameters that are not included in an open loop estimate, and modeling errors. Further, by adapting the model during certain conditions, it is possible to compensate for errors caused by other factors, such as offsets in the fuel injectors at a time when pump flow estimation errors do not exist (since the pump is not operating). Then, when the pump is operating and adaptation is enabled, the present invention can assign any error to estimations in pump flow. In this way, a robust control system can be obtained.
Note that various types of adapative parameters can be used. For example, a single parameter can be used that accounts for all modeling error. Alternatively, adaptive data across various engine or environmental operating conditions can be used.